checkpatch: add a --fix-inplace option

Add the ability to fix and overwrite existing files/patches instead of
creating a new file "<filename>.EXPERIMENTAL-checkpatch-fixes".

Suggested-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Joe Perches <joe@perches.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Cc: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>